In Nero Wolfe "Before I die", the gangster's sidekick asks for spaghetti and gravy. After Wolfe's chef Fritz prepares him spaghetti with the type of gravy used for roast beef, it turns out that the gangster meant tomato sauce when he said gravy. Looking on the internet there is a lot of confirmation that some Italian-Americans use "spaghetti and gravy" to mean spaghetti with a tomato-based sauce, for example discussions like this:
At the bottom there is an answer like so:
I think the Italian Immigrants in New Jersey put their own spin on a lot of things.... [Gravy] is an Italian American invention. I never heard red sauce called gravy until I roomed in college with my Italian roomate from Hoboken.
Gravy is one of those words where Italian immigrants picked the closest word to their native word. My father was born in Naples (Italy, not Florida) and called it gravy. That's good enough for me.
Can anyone confirm or deny this? What is the origin of using gravy to mean spaghetti sauce?
(Apologies for yet another spaghetti question.)